This is not a simple question to answer but this is what I believe. To find out if you are in love with someone you have to ask yourself if you would be unhappy if that person was not in your life. The unhappier this makes you feel, the more you will know that you love them. It’s the same with anything though; not just people. If you have a hobby, or a pet, or just a dream; you ask yourself the same question, and this will tell you how much you love the hobby or the pet or the dream, or anything else. I love writing for example; because I know that if I could not write I would be very unhappy. Of course if you love someone and they do not feel the same as you, it becomes complicated and can cause unhappiness. But if two people ask the same questions about each other and then realise that they are both feeling love – that’s beautiful.

Also, "How do you know you've been loved by someone?"

Thanks for your help. It's "How do you know if you've loved someone?"

? :)

你的问题时“你怎么知道你爱过有人”(How do you know if you've loved someone?) 或是“你怎么知道有人爱过你” (How do you know if someone has loved you?)